Process for removing catalysis inhibitors from aqueous solutions



Patented Jan. 14, 1936 UNITED STATES PATENT OFFICE PROCESS FOR REMOVINGCATALYSIS IN- HIBITORS FROM AQUEOUS SOLUTIONS Henry F. Johnstone,Urbana, Ill., assignor to Board of Trustees of the University ofIllinois, Urbana, 111., a corporation of Illinois No Drawing.Application August 18, 1933, Serial No. 685,747

7 Claims. (Cl. 204-9) This invention relates to a process for relationof the water through brass fittings or solmoving catalysis inhibitorsfrom aqueous soludered connections, tend to destroy the effectivetions,and more particularly is directed to the, ness of the catalyst.

removal of phenolic compounds and certain While the primary object ofthe present procmetallic salts which inhibit catalytic oxidation ess isto remove these inhibitory compounds reactions in water or aqueoussolutions. from such solutions because of their interfer- In mycopending application, Serial No. ence with catalytic oxidation, ofwhich the oxi- 500,684, filed December 8, 1930, I have described dationof dissolved sulphur dioxide is only cited in detail a process forremoving sulphur-dioxide as one example, it is to be understood that the10 from fiue gases or other waste gases. In that process is not limitedto such solutions, but it 10 process, the sulphur dioxide bearing gas ismay be used for the removal of phenolic compassed through a washing orscrubbing tower, pounds from any volume of water in which they Where itis contacted by an aqueous Washing may be present in smallconcentrations. This solution and is absorbed into the solution, beingincludes the treatment of factory wastes which then oxidized tosulphuric acid. The solution contain phenolic compounds, and watersupplies 15 preferably contains manganese or iron sulphate, which arecontaminated with such wastes, as or both, which act as catalysts toincrease the well as all other types of solutions having such oxidationof the absorbed sulphur dioxide, in compounds therein. order to retainthe solution at its maximum In the preferred form of carrying out myabsorbing capacity. Preferably oxygen, or an invention, the process forpreventing the in- 20 oxygen-bearing gas, is also passed through thehibitory action of these compounds consists in tower, to decrease thesulphur dioxide-oxygen destroying or removing the inhibitor byelecratio, whereby the reaction proceeds more trolysis under definitelycontrolled conditions. rapidly. Simultaneous absorption of these twoThese conditions are determined by the chargases in the solution isfollowed by their interacter and concentration of the inhibitors, the 25action in the presence of a metallic ion catalyst. temperature of theaqueous washing solution or Such interaction removes the sulphurdioxide, water solution, the type of catalyst which is as such, from thesolution, increasing the cabeing used, and the rate of flow of thesolution pacity of the solution for absorbing this gas. through theelectrolytic cell. Thus, in carrying 3 However, I have found that inpractice, the out the invention, I preferably maintain a direct processmay be materially slowed down or incurrent between lead or other inertelectrodes hibited by the presence of certain compounds at an anodiccurrent density which is determined which interfere with the operationof the cataby the concentration of the phenolic compounds lyst. Thesecompounds, commonly known as or other inhibitors in the water and therate at inhibitors or negative catalysts, are active even which thewater or solution flows past the elec- 35 when present in extremelysmall concentrations. trodes. The electrolytic oxidation which takes Inthe particular oxidation reaction outlined place at the anode eitherdestroys the inhibitor above, which has been taken by way of exampleentirely as in the case of the phenolic comonly, as the process of thepresent invention is pounds, or renders it inactive as in the case ofequally applicable to other than the oxidation of stannous salts, whichare converted to stannic sulphur dioxide in water in the presence of asalts, where they are no longer inhibitory in metallic ion catalyst,some of the inhibitors action. In the case of copper salts, the inwhichprevent catalysis are the phenols, cresols, hibitory action is preventedby the deposition hydroquinone, and other members of the phenol of themetal on the cathode, in which case a group, including monohydric,polyhydric and sufiicient' electromotive potential and cathodic 45substituted phenols. As a result of the incomcurrent density is requiredto deposit the metal, plete combustion of coal, a number of these whichcan be readily determined from the concompounds may be present in theflue gases. centration of the salt in the solution.

Beside these organic inhibiting substances, there In order to increasethe effectiveness of the are several metallic salts that have been foundelectrolytic action, I have found that the de- 50 to inhibit thecatalytic oxidation of sulphur struction of the phenolic compound may beacdioxide, especially when a manganese salt is -celerated by theaeration of the solution simulused as the catalyst. For example, certaincoptaneously with its electrolysis. per salts and stannous salts, whichmay be pres- Also, the electrolysis must be governed to ent in thescrubbing water'as a result of circusome extent by the type of catalystwhich is 55 being employed in the oxidation reaction. In the case of amanganese salt as a catalyst, it is necessary to prevent the removal ofthe catalyst itself, which occurs by the electrolytic deposition of themanganese dioxide upon the anode of the cell; I have found that this maybe prevented by maintaining the solution at a temperature of at least 50degrees centigrade during the electrolysis, which prevents the removalof the catalyst, while in no way affecting the destruction or removal ofthe inhibitory substances.

I have found that there is apparently no limit to the amount of theinhibitory substance which the current will remove provided that asuflicient current density is used at the time that the contaminationoccurs, and that a sufficient time is allowed, or the solution issufficiently aerated in addition to the electrolysis, to provide fordestruction or removal of the inhibitors. Under any of these conditionsthe inhibitors, either phenolic substances, or other oxidizable organicor inorganic substances, or copper salts, are completely removed fromthe catalytic solution, and the efliciency of the catalyst is retainedinthe solution.

In practice, such as in the use of the present invention in the removalof inhibitors from the washing solution used for absorbing sulphurdioxide from flue gases and the like, I preferably provide anelectrolytic cell and aerator in the path of the washing solutionleaving the washing tower. As the solution passes through the cell, itis simultaneously electrolyzed and aerated, the electrolytic action uponthe solution which is circulating between the two electrodes of the celldestroying the inhibitors in the solution. The solution, as it leavesthe washing tower, will have therein the inhibitors, whether they bephenolic compounds or other substances absorbed from the flue or wastegases, or whether they be metallic salts carried into the solution fromvarious pipe fittings or connections. The temperature of the solution,if a manganese salt is used as a catalyst, must be maintained at atemperature of at least 50 degrees centrigrade to prevent the removal ofthe catalyst. The electrolytic cell is connected to a suitable source ofdirect current, which is capable of maintaining a sufficient currentdensity on the anode, or cathode, to destroy the inhibitor in thesolution effectively.

In carrying out the invention, I have found that a predetermined minimumcurrent density is required to remove the inhibitor, this cur-,

rent density depending upon the character and concentration of theinhibitor. For example, the addition of one part per million ofhydroquinone to a washing solution for absorbing sulphur dioxide fromflue gases requires a current density of 0.15 amperes per square inch todestroy the inhibiting action thereof, if the current is flowing whenthe inhibitor is added or absorbed into the solution and is continuedfor at least twenty seconds thereafter. Hydroquinone is one of the mostpowerful inhibitors of the phenolic group. With this current densitymaintained, as much as three parts per million of hydroquinone may beadded at intervals as short as forty-five seconds apart without causinginhibition of the catalytic reaction. If the rate of addition isgreater, 2. longer period of electrolysis is required.

If the oxidation reaction in the solution has once become inhibited, amuch longer time, in some instances twelve to twenty minutes, isrequired to remove the inhibitor and regain the original efliciency ofthe catalytic reaction. Also, I have found that when a solution hasbecome inhibited, the catalytic activity can be regained quickly byshutting off the flow of gas or other substances being oxidized, andaerating the solution during the electrolysis.

It is apparent, therefore, that by providing an electrolyzing andaerating process such as described, catalytic inhibition of theoxidizing reaction can be prevented. A current density may be maintainedin accordance with the character and. concentration of the inhibitorswhich will normally be present, and, by allowing a suflicient time foreach part of the solution to be electrolyzed, or by aerating thesolution simultaneously with its electrolysis, the inhibitors, whetherthey be phenolic substances, or other oxidizable organic or inorganicsubstances, or copper salts, can be completely removed from thesolution, and the catalyst, can be maintained at a high efficiency foraiding the oxidation reaction.

While I have described the application of my novel process for theremoval of catalysis inhibitors in a scrubbing solution used to removesulphur dioxide from flue gases and the like, it is to be understoodthat I do not intend to limit my invention to this specific use of theprocess, inasmuch as the invention is equally useful in other fields inwhich it is desired to remove phenolic compounds or other inhibitorsfrom water or aqueous solutions. I therefore intend to be limited onlyin so far as defined by the scope and spirit of the appended claims.

I claim:

1. The method of removing phenolic compounds from aqueous solutionswhich comprises subjecting the solutions to direct current electrolysis,simultaneously aerating said solutions, controlling the anodic currentdensity in accordance with the character of the phenolic compounds tocompletely remove said compounds by oxidation from said solution, andcontrolling the rate of flow of said solution in accordance with theconcentration of said compounds.

2. The method of removing phenolic compounds from aqueous solutions ofan oxidation catalyst which comprises subjecting the solutions to directcurrent electrolysis, and controlling the anodic current density and therate of flow of said solutions in accordance with the character andconcentration of the phenolic compounds to completely remove saidcompounds from said solution by oxidation and to prevent removal of saidcatalyst.

3. The method of removing phenolic compounds from aqueous solutions ofan oxidation catalyst including manganese salts which comprisessubjecting the solutions to direct current electrolysis, controlling theanodic current density and the rate of flow of said solutions inaccordance with the character and concentration of the phenoliccompounds to completely remove said compounds from said solution byoxidation, and controlling the temperature of said solutions to preventthe removal of said catalyst.

4. The method of removing phenolic compounds from aqueous solutions ofan oxidation catalyst including manganese salts which, comprisessubjecting the solutions to direct current electrolysis, maintaining aminimum temperature of 50 centigrade in said solutions to preventremoval of said catalyst, and controlling the rate of flow of saidsolutions and the current density for said electrolysis in accordancewith the concentration of said compounds to completely remove saidcompounds from said solution by oxidation.

5. The method of removing oxidizable organic catalysis inhibitors fromflowing aqueous solutions having catalytic oxidation ions therein, whichcomprises subjecting said solutions to direct current electrolysis, andcontrolling the anodic current density during said electrolysis inaccordance with the character and concentration of said inhibitors andthe rate of flow of said solutions to completely remove said inhibitorsfrom said solution by oxidation.

6. The method of removing phenolic catalysis inhibitors fromsulphur-dioxide absorbing solutions having an oxidation catalyst thereinfor increasing the rate of absorption of said sulphurdioxide, whichcomprises subjecting said solution to direct current electrolysis,controlling the current density during said electrolysis in accordancewith the character and concentration of said inhibitors, and maintainingthe temperature of said solutions at a predetermined minimum to preventremoval of said catalyst.

'7. The method of removing inhibitors comprising any one of thefollowing group, namely, phenols, cresols, and hydroquinonafrom aqueoussolutions having catalytic ions therein, which 10 comprises subjectingsaid solutions to direct current electrolysis, and controlling theanodic current density in accordance with the character andconcentration of said inhibitors to oxidize said inhibitors foreffecting their complete re- 15 moval from said solutions whilemaintaining said catalytic ions in said solutions.

HENRY F. J OHNSTONE.

